Read this (after a quick Google search)
http://bryophytes.science.oregonstate.edu/page20.htm
Chemical Control of Moss on Trees and Shrubs
Chemical control of mosses on trees and shrubs is not commonly attempted by the average homeowner because these products are fairly toxic and require use of special protective equipment when handling them. You may want to hire a professional if you desire to remove mosses from trees and shrubs using chemicals.
Control of mosses is generally achieved using either copper sulfate or lime sulfur. Professional tree care companies and the Oregon State Extension Service recommend these chemicals as effective treatments. Even though they may be effective in killing the moss, the effect is short lived. Furthermore, the treatment is unnecessary, because mosses are benign and do not parasitize the trees and shrubs. Why use these polluting chemicals if they are unnecessary?
Chemicals are sprayed on the mosses during the winter dormancy period. They can damage leaves if applied during active growth and can also damage evergreen leaves and needles. They are corrosive, so care must be taken to keep them from drifting onto painted or metal surfaces. These chemicals should only be used according to the label and should only be used on plants that are listed on the label (Davison and Byther, 1999).
Copper Sulfate
Copper sulfate is often used as a fungicide or algaecide, but it can also work to control mosses if used during the dormant period when the plant is not growing. It is available as a dust, wettable powder and fluid concentration. It is used primarily by farmers and may not be available at all stores. Tri- Basic copper sulfate and Bordeaux (copper sulfate formulated with lime) are formulations that have been used to control mosses on trees and shrubs. There are a lot of products available and you should consult labels before attempting to use any of them. A sprayer is generally used to apply copper sulfate on to trees.
Effectiveness
Copper sulfate is effective at killing mosses when used properly. It works by disrupting photosynthesis. It will also damage plants, especially if they are in active growth. You will have to continue applying it every few years if you don't improve cultural conditions like sunlight and air circulation because the mosses will return. The dead mosses will also persist after spraying for a while before they weather and fall off the branches.
Side Effects
Copper sulfate is a moderately toxic product and care should be taken when handling this pesticide. Poisoning and even death has been attributed to ingestion of copper sulfate (EXTOXNET web site). Protective equipment including long sleeve clothes, mask and safety glasses should be used (Meister, 1996). Chronic effects that have been documented include liver disease and anemia due to long term exposure to applicators over several years. Refer to EXTOXNET web site for more details. This product can also be harmful to wildlife, especially aquatic organisms like fish. Copper sulfate should not be used near creeks or bodies of water.
Lime sulfur
Lime sulfur is used as a fungicide but is also effective in controlling mosses when used during the winter months that mosses are actively growing and the trees or shrubs are dormant. It is used primarily by farmers and may not be available at all stores. You should consult labels before attempting to use it. You will use a sprayer to apply it to trees. It smells like rotten eggs.
Effectiveness
Lime sulfur is effective for controlling mosses on trees and shrubs. You will need to reapply it every few years if you do not address the causes of moss growth.
Side-Effects
This product is very toxic. It can cause permanent damage to the eyes. Protective equipment including a respirator, safety glasses and long sleeve clothes should be worn (Meister, 1996). This product is corrosive and will cause damage to painted surfaces. There is less information available on the effects to wildlife. This product is also used as an insecticide and may harm beneficial insects like honeybees. It persists on the plant for a while by leaving a sulfur residue after it dries. This will wash off after winter rains.
